Volume 368, Number 2, March III 2001
|Page(s)||420 - 430|
|Section||Cosmology (including clusters of galaxies)|
|Published online||15 March 2001|
BeppoSAX spectroscopy of the luminous X-ray sources in M 33
Astrophysics Division, Space Science Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands
2 Dept of Physics & Astronomy, University of Southampton, Southampton, Hants, SO17 1BJ, UK
3 Astronomical Institute "Anton Pannekoek", Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
4 XMM-Newton SOC, ESA Villafranca, Apartado 50727, 28080, Madrid Spain
5 Observatory & Astrophysics Lab., University of Helsinki, Helsinki, Finland
6 Max-Planck-Institut für Extraterrestrische Physik, 85740 Garching bei München, Germany
7 Osservatorio Astronomico di Brera, Via Bianchi 46, Merate 22055, Italy
Corresponding author: A. N. Parmar, firstname.lastname@example.org
Accepted: 18 December 2000
The nearby galaxy M 33 was observed by the imaging X-ray instruments on-board BeppoSAX. Two observations at different phases of the 105.9 day intensity cycle of the luminous central source X-8 failed to reveal the expected modulation, suggesting that it is probably transitory. Similar behavior has been observed from several X-ray binary sources. This strengthens somewhat the idea that M 33 X-8 is a black hole accreting from a binary companion. The 0.2-10 keV spectrum of M 33 X-8 can best be modeled by an absorbed power-law with a photon index, α, of and a disk-blackbody with a temperature, kT, of keV and a projected inner-disk radius of km. This spectral shape is in good agreement with earlier ASCA results. The 2-10 keV spectra of M 33 X-4, X-5, X-7, X-9 and X-10 are all consistent with power-law or bremsstrahlung models, whilst that of X-6 appears to be significantly more complex and may be reasonably well modeled with a disk-blackbody with keV and a projected inner-disk radius of km. The spectrum of M 33 X-9 is rather hard with . Compared to earlier Einstein and ROSAT observations, M 33 X-7 and X-9 varied in intensity, M 33 X-4, X-6, and X-10 may have varied and M 33 X-5 remained constant.
Key words: galaxies: individual (M 33) / galaxies: nuclei / X-ray: galaxies
© ESO, 2001
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